X-ray Absorption Spectroscopy of Dimethyl Sulfoxide Reductase from Rhodobacter sphaeroides

X-ray absorption spectroscopy at the molybdenum K-edge has been used to probe the molybdenum coordination of Rhodobacter sphaeroides dimethyl sulfoxide reductase. The molybdenum site of the oxidized protein possesses a novel Mo(VI) mono-oxo site (MoO at 1.68 Å) with additional coordination by approximately four thiolate ligands at 2.44 Å and probably one oxygen or nitrogen at 1.92 Å. The reduced Mo(IV) form of the enzyme is a des-oxomolybdenum with 3−4 thiolates at 2.33 Å and two different Mo−O/N ligands at 2.16 Å and 1.92 Å. Similarly, the stable Mo(V) glycerol-inhibited species is found to be a des-oxomolybdenum with approximately four thiolate ligands at 2.40 Å and (probably) two similarly coordinated oxygen or nitrogen ligands at 1.96 Å.